The present invention relates to an apparatus for maximizing energy management in xe2x80x9csoftxe2x80x9d hybrid vehicles having multiple energy storage sources.
The need for reduced vehicle emissions, increased fuel economy, increased electrical loads and better energy management has driven major automotive original equipment manufacturers (OEMs) to consider xe2x80x9csoftxe2x80x9d hybrid vehicles as one potential solution. A xe2x80x9csoftxe2x80x9d hybrid vehicle typically has an electric drive motor/generator unit operating at a higher voltage (e.g., 42V) coupled in parallel with a conventional internal combustion (IC) engine, which engine may be downsized to some degree. The motor/generator, also referred to as an Integrated Starter-Generator or ISG, takes the place of the conventional starter and alternator used with the IC engine, and performs additional functions including, but not limited to, torque assist, regenerative braking, automatic start-stop, power boost, and limited traction.
The move towards hybrid vehicles introduces a second torque source on the vehicle (in addition to the conventional IC engine), and systems and strategies are needed to coordinate these torque sources to meet the various vehicle application demands. The presence of an ISG allows the IC engine to be shut down when it is not needed for propulsion, recover the energy typically lost in braking, and use the energy from an energy storage system when additional power is needed in situations such as starting a vehicle from rest, or for merge or overtake situations. The energy storage system on the hybrid vehicle must meet the diverse requirements that each of the above-identified modes of operation demand, while still satisfying the conventional demands of the vehicle electrical system. A battery is well suited to meet the conventional energy requirements of vehicle operation such as supporting the electrical loads on the vehicle. A capacitor, on the other hand, is well suited to support transient situations requiring high power, e.g., torque boost to aid the engine in merge and overtake situations, or to recover the energy lost during braking (regeneration). These storage devices need to be managed appropriately depending on the mode of operation of the vehicle.
The present invention concerns an apparatus for providing electrical power for a hybrid vehicle including: an integrated starter-generator connected to an inverter; a capacitor means for storing electrical energy; a first switch means connected between the inverter and the capacitor means, or any other form of electrical energy storage means; a battery means for storing electrical energy; a second switch means connected between the inverter and the battery means; and a control means connected to the first and second switch means for selectively turning each of the first and second switch means o n and off The control means turns each of the first and second switch means on and off to charge the battery means from the capacitor means by pulse width modulation. The control means turns the first switch means on to provide electrical power from the capacitor means to operate the integrated starter-generator. The control means turns the second switch means on and of by pulse width modulation to charge the battery means from the integrated starter-generator.
The first switch means can include a diode permitting current flow from the inverter to the capacitor. The second switch means can include a diode permitting current flow from the battery to the inverter and the capacitor.